YAMAMOTO Mitsuharu's patch for pdf-tools on MacOS https://lists.gnu.org/archive/html/emacs-devel/2016-04/msg00648.html

retina.patch

diff --git a/lisp/pdf-annot.el b/lisp/pdf-annot.el
index b0ff3c2..82cf122 100644
--- a/lisp/pdf-annot.el
+++ b/lisp/pdf-annot.el
@@ -981,6 +981,7 @@ other annotations."
                (pdf-cache-renderpage-highlight
                 page (car size)
                 `("white" "steel blue" 0.35 ,@edges))
+            :width (car size)
              :map (pdf-view-apply-hotspot-functions
                    window page size))))
         (pdf-util-scroll-to-edges
diff --git a/lisp/pdf-info.el b/lisp/pdf-info.el
index 3eeacf8..54c07e5 100644
--- a/lisp/pdf-info.el
+++ b/lisp/pdf-info.el
@@ -1594,7 +1594,15 @@ Return the data of the corresponding PNG image."
     'renderpage
     (pdf-info--normalize-file-or-buffer file-or-buffer)
     page
-    width
+    (* width
+       ;; XXX This does not give optimal results when you have both
+       ;; Retina and non-Retina displays connected.  For true
+       ;; high-resolution support, one should use either TIFF, "@2x"
+       ;; convention, or resolution-independent formats such as PDF.
+       (or (and (memq (pdf-view-image-type) '(imagemagick image-io))
+               (fboundp 'frame-monitor-attributes)
+               (cdr (assq 'backing-scale-factor (frame-monitor-attributes))))
+          1))
     (let (transformed)
       (while (cdr commands)
         (let ((kw (pop commands))
diff --git a/lisp/pdf-isearch.el b/lisp/pdf-isearch.el
index 563e721..5225395 100644
--- a/lisp/pdf-isearch.el
+++ b/lisp/pdf-isearch.el
@@ -742,7 +742,7 @@ MATCH-BG LAZY-FG LAZY-BG\)."
                                  occur-hack-p)
                              (eq page (pdf-view-current-page)))
                     (pdf-view-display-image
-                     (pdf-view-create-image data))))))))
+                     (pdf-view-create-image data :width width))))))))
       (pdf-info-renderpage-text-regions
        page width t nil
        `(,fg1 ,bg1 ,@(pdf-util-scale-pixel-to-relative
diff --git a/lisp/pdf-view.el b/lisp/pdf-view.el
index 2eecb8e..7e6af5a 100644
--- a/lisp/pdf-view.el
+++ b/lisp/pdf-view.el
@@ -892,7 +892,7 @@ See also `pdf-view-set-slice-from-bounding-box'."
   "Return the image type that should be used.
 
 The return value is either `imagemagick' (if available and wanted
-or if png is not available) or `png'.
+or if png is not available), image-io (on the Mac port), or `png'.
 
 Signal an error, if neither `imagemagick' nor `png' is available.
 
@@ -900,6 +900,8 @@ See also `pdf-view-use-imagemagick'."
   (cond ((and pdf-view-use-imagemagick
               (fboundp 'imagemagick-types))
          'imagemagick)
+        ((image-type-available-p 'image-io)
+         'image-io)
         ((image-type-available-p 'png)
          'png)
         ((fboundp 'imagemagick-types)
@@ -909,8 +911,8 @@ See also `pdf-view-use-imagemagick'."
 
 (defun pdf-view-use-scaling-p ()
   "Return t if scaling should be used."
-  (and (eq 'imagemagick
-           (pdf-view-image-type))
+  (and (memq (pdf-view-image-type)
+             '(imagemagick image-io))
        pdf-view-use-scaling))
 
 (defmacro pdf-view-create-image (data &rest props)
@@ -1377,7 +1379,8 @@ This is more useful for commands like
               `(,(car colors) ,(cdr colors) 0.35 ,@region))
            (pdf-info-renderpage-text-regions
             page width nil nil
-            `(,(car colors) ,(cdr colors) ,@region)))))))
+            `(,(car colors) ,(cdr colors) ,@region)))
+       :width width))))
 
 (defun pdf-view-kill-ring-save ()
   "Copy the region to the `kill-ring'."